Rare earth separation by adsorption and desorption



vaiueof the range: acid co'ncentration a: suitable pH is at or-near.-

Patented Jan. 23, 195 1 ICE 2,539,282= RARE EARTH SEPARATIQNBYADSORP TION AND DESORBTIOM Frank H. Spedding and Adolf'" F; Voigt; AiilS; Iowa, ass'ignors to the United States of Aine'ricaas represented by the United statesnttmienm ergy' Commission Nb Drawing. Application March. 23, 1949; Serial- No. 83,098

42 Giants. 1

This inventionrelates-to theseparation of rare earths-.-

For many years one of themost difli cult proc-' esses in the field of chemistry has. been the saparation of rare. earths-trom'each other inthein pure states. Their chemical and';phyical.prop.- erties are so similar that in generai a single operation leads only toa partial separation or enrichment. In general, the best means of separating these elements has beenthe: welleknown but laborious method of fractional crystallization; Exceptions are cerium with its tetravaient state, and samarium, europium and ytterbium with their divalent stateswhichdo, permit a means of p ration. from the. normal trivalent rare earth ions.

It is, an object. of. this invention to provide a process for the separation of rare earths.

It is another object of this inventioncto provide a process for the separation of immediately adjacentrrare earths.

Other objects will be. apparenti from: the; following description.

We have'found-that rare earths, evenimmediately adjacent rare' earths; can" be separated to produce rare earths o1? high purity by adsorbing a-mixtur-e of the rare earths fromaqueouszsolu tionsof their water-soluble inorganic salts, pref erably chlorides, on a cation exchange. resin and.

mm onstacitric-acid'and lias' ak pr nce: 225% 7:0; This-pH is obtained suitably by the additi'o or ammonia or" ammonium-2 hydroxide,

as concentrated ammomum hydroxide; to

produce=an =ainmonium citrate-citric acidbuffer;

At the higher concentrations of citricv acid a suitable solution has a-pH at or near the lower At an intermediate citric the intermediate value of the range and at the; lower citric acid concentration, the suitable pH is" at or nearthe highervalue-of the pH range. Using a 5% citric acid solution; as. suitable pH range for the-solutionis:from225' to 3.0 and the preferred pH range is between 2.5' and'2.8. Using a 0.5% citric acidnsolution a suitable pH range for the solution is betwe'en 3.5 and 4 .5 and the preferred pH rangeiis between 39 and &.3. Using a 0.1% citric acid-solution a suitable pH range for the solution is-between 4.5 and 7.0 and the preferred pH range is between 5.0 and 6.5. There are slight variations in the preferred range depending upon whether the'process is used for the separationgof: light rare .earthelements (members of; the. cerium group) or. heavyrare earth.

elements; (members or; the yttrium group) Eon;

example;-, using; 0. 1%; citric acid, the. p ieferredi for the separation of thelight rare' earth elements and-.5.l to :6.5 for the separationof heavy; rare earth elementsby the process of the present: invention. The citric acid concentration used herein refers to weight percent citric acid, erg. 5% citric acid solution refers to grams on. citric acid monohydrate per liter of solution.

When the pH: is adjusted'by the addition of am-fmonia. or ammonium hydroxide to the desired pH; thecitric acid-solution will not contain all; OfTthSCltI'iC acid -asfree acid; part of it is then. present as ammonium citrate; Fora particular. eluting solution the suitable -p H will depend upon, the citric acidconcentration; the suitable pH. issufiiciently highto-elute adsorbed rare earths and yet is sufiiciently low to efiectuate-the selec-' tive elution accomplished bythe processof the subject invention.

A; preferred. cation exchange a resin is a sul-. fonated synthetic organiccation exchange resin.. A sulfonated phenol-formaldehyde typeof resin, which may be a-resinprepared from a naturaloccurring phenoliczma terial such as tannin, orprepared from a synthetic phenolic compound, is suitable example of thistype of sulfonatedl synthetic organic cation exchange resin. The sulfonated phenol-formaldehyde type of resin. usually containsthesulfonic: acidgroups linked to the aromatic rings. each through amethylene radical. Another preferred sulfonatedsynthetic; organic cation exchange. resin is a nuclear sullfonic type of. synthetic organic cation exchangeresinin which the sulfonic acid groupsfare-di-e rectly attached toth aromatic nuclei in anarcmatic hydioca'rbon polymer.

In one embodiment of thisinverition an.aquous solution of Water-soluble inorganicsalts or. rare earths is added to a column ot catio'n exchange resin to adsorb the rare'earth ions an'd. the citric acid solution as eluant is passed through the column of adsorbed resin. In the simple case, where the rare. earth mixture contains only ttt'o rare earths, successive portions .ofeluate are col: lected; and the first portions; containing des'o'rbed rare earth ions, are solutions of one rareearthof high-purity; Intermediate portions of. the eliiate, containnihrtur'es' of the rear earths and a final portionof the eluate containsthe other rarefearthof high purity. The intermediate portions may. be treated to obtain an aqueous solution .of awater-soluble inorganic. salt ,of

the mixedrare earths and" the resultant solution: subjected to the process of this invention for a. further separation of rare.earths.. In the case. of the separation of, neodymium and praseodymium the first portion of eluate c'ontainsneodymium of high purity. The intermediate portion contains. a mixture of :neodymium and prasee odymium and thefinalportion contains praseodymium of high purity; In the preferred oper ation of this embodiment the co1umn of= resin is of such length that less than 20% of the bed is utilized for adsorption, so that the lower unadsorbed portion of resin is utilized for eflicient separation of the rare earths during the desorption step, when citric acid is passed through the column for elution. In other words, the preferred amount of resin used is at least 5 times the amount required to adsorb all rare earth ions.

In another embodiment of this invention a solution of a mixture of Water-soluble inorganic salts of rare earths is contacted with the resin and this adsorbed resin is placed in a column above unadsorbed resin and the citric acid solution is passed through the column.

In a third embodiment of the present invention the rare earth ions are adsorbed on the resin and eluted therefrom by the citric acid solution. The total eluate is then passed through a bed of resin and successive portions of the eluate are collected.

In a fourth embodiment a mixture of rare earths adsorbed on a cation exchange resin is separated by passing the eluant of this invention through a column of the resin containing the rare earth values, passing the eluate through a column of cation exchange resin, and collecting successive portions of the eluate from the resin that initially contained no adsorbed rare earths.

The following examples illustrate the process of this invention.

The synthetic organic cation exchange resin used in Examples I, II, and III was Amberlite IR-l, a sulfonated phenol-formaldehyde type of cation exchange resin in which the phenolic compound was a natural-occurring material, namely, tannin. In Examples IV through VII the resin is Amberlite IR-100, a sulfonated phenol-formaldehyde type of resin made from a synthetic phenol. Both of these resins are of the phenolic methylene sulfonic type of cation exchange resin. In Examples VIII through XVI the resin was either Amberlite IR-lOO, Dowex 50, or Nalcite I-ICR, the latter two being examples of the nuclear sulfonic type of synthetic organic cation exchange resin. According to the article, J. Am. Chem. Soc. 69, 2830, Dowex 50 is an aromatic hydrocarbon polymer of the type described by DAlelio in U. S. Patent 2,366,007 containing nuclear sulfonic acid groups as the sole ion-active group at any pH value. According to Table I in the article, Analytical Chemistry, 21, 87, at page 89, Nalcite HCR and Dowex 50 are both the nuclear sulfonic type of synthetic organic cation exchange resin.

In Examples I through VII the cation exchange resin was first screened to remove particles greater than 20 mesh and then soaked in water. The resin slurry was added to the column and backwashed with water to remove fine resin particles, which would otherwise plug the column and thereby reduce the flow rate. In Examples I through V the resin in the column was conditioned as follows: A 5% hydrochloric acid solution was passed through the column converting the resin to the acid cycle, using a contact time of at least thirty minutes to insure complete conversion. A 2% sodium chloride solution was passed through the column to convert the resin to the sodium cycle. This treatment with acid and salt was repeated at least two more times with the resin being left finally in the acid cycle.

. EXAMPLE I Using a 16-mm. column having a resin bed length of 175 cm., an aqueous solution, containing praseodymium and neodymium chlorides, in which the rare earth content was 21% praseodymium and 79% neodymium, was introduced into the top of the resin bed to provide a weight of adsorbed rare earth ions totalling 0.65 g./cm. of cross-section of the column, with the weight of rare earth ions calculated as rare earth oxide. An aqueous solution containing 5% citric acid adjusted to a pH of 2.53 by the addition of concentrated ammonium hydroxide was passed through the column and successive eluates were collected and analyzed for neodymium and praseodymium content. An identical experiment was carried out in which the pH of the citric acid solution was 2.75. In a similar series of experiments the pH values of citric acid solutions were 2.55 and 2.65 and the weight of adsorbed rare earth was 0.5 g. (calculated as oxide)/cn1. of

cross-section of the column. The rare earth content used in this series was 43.4% praseodymium and 56.6% neodymium. Data for these four runs are shown in Table I. In all cases the flow rate of eluant was maintained between 5 and 6 cm./min.

Table I Per cent Per cent Purity of Eluted Nd Eluted pH 2 53 pH 2.75 pH 2.55 pH 2.65

10 99. 2 95. 0 95.6 39.1 20 97. s 93. 2 94. 5 s9. 1 30 97.1 91. o 93. 9 99.1 49 95.5 89.4 92.8 87 3 5o 95. 9 s9. 4 91.1 84. 9 60 95. 1 88. 4 89. 1 s2. 5 7o 94. 0 88. 4 s7. 0 79. 5 90 84. o 77.8 99 79. 5

These data show that pH has a marked effect on degree of separation and that for the preparation of rare earths of high purity it is necessary to use a citric acid solution having a pH within a narrow range.

EXAMPLE II Using a 49-min. column with a resin bedlength of 850 cm. and a mixture of rare earth chlorides, with a rare earth content of 79.5% neodymium, 18% praseodymium and 2.5% samarium, the rare earth mixture was adsorbed on the resin as in Example I. A 5% citric acid solution at a pH of 2.65 was used for elution. The flow rate of the citric acid solution was 5 cm./min. Table II below illustrates that the first portions collected of the eluate contained neodymium of high An aqueous solution of a 50-50 mixture of neodymium and praseodymium chlorides was introduced into a 16-min. column containing a resin I bed length of cm. to adsorb the rare earths.

A 5% citric acid solution with a pH of 2.55 was Table VI Fraction Approximate Composition column containing Amberlite IR-lOO resin in the acid cycle having a resin bed height of 120 cm. The resin was 30, +40 mesh, that is, the

resin passed through a size 30 screen and was,

retained on a size 40 screen. Quantities of a 0.1%

citric acid solution having a pH of 5.5 were prepared by dissolving 4.5 g. of citric acid mono- These examples illustrate that rare earths of high purity can be obtained by the process of this invention.

The same process as described above has been applied to the separation of members of the heavy rare earths, yttrium group, consisting of the elements between gadolinium and lutecium, inclusive.

EXAIVLPLE VII A rare earth oxalate mixture had a 40% loss on ignition at 800 C. Analysis of the residue, with weight percent of oxide based on percent of original oxalate, was as follows:

% C802 3% DyzOs 7% Nd203 02-05% Er203 5% SmzOs 0.20.5% H0203 6% Gd203 10% $102 YzOs The oxide produced by ignition of the oxalate mixture for eight hours at 800 C. was placed in a vessel with double its volume of 6 N H01, and the acid refluxed for two hours. A large excess of water was added and the supernatant liquid decanted and, after further dilution to an acid strength of 0.5 N or less, the rare earths therein were precipitated by the addition of oxalic acid. The precipitate was ignited to the oxide and an aqueous solution of the rare earth chlorides was prepared therefrom. A 100-gram sample of the acid-extracted rare earths was adsorbed on an 8-ft. bed of resin in a 4-in. column and a 0.5% citric acid solution at a pH of 3.9 was passed through the column. The elution data are shown below in Table VII.

hydrate, 45 g. of phenol and about 33 m1. of concentrated ammonium hydroxide in 45 1. of dis- 10 tilled water. The resultant 0.1% citric acid solution was passed downwards through the column at a flow rate of 0.5 cm./min. After 32.5 1. of eluate had been collected, the subsequent portions of eluate contained varying amounts of rare earth salts. Quantities, each 0.5 1., of the eluate were collected after 32.5 1. had been collected and these 0.5-1. fractions were analyzed for total rare earth content. The percentages of neodymium and praseodymium in a number of the fractions were determined. From the analytical data, it was determined that 81.7% of the original Nd content of the mixture was collected, in the first eluate fractions containing rare earth values, as pure neodymium and that 82.7% of the original eluate fractions as pure praseodymium. The intermediate fractions contained varying ratios of neodymium and praseodymium.

Two similar adsorption-elution experiments were carried out adsorbing in each case 1.695 g. of the same rare earth mixture and using Amberlite IR-lOO with the same mesh size in a 22- mm. column having a resin bed height of 120 cm. In both experiments 0.1% citric acid solution containing 0.1% phenol and having a pH of 5.5 was used; however, the flow rates in these experiments were 1.0 and 2.0 cm./min. In the experiment with the flow rate of 1.0 cm./min., the analyses of eluate fractions showed that eluate fractions were obtained which contained 69.3% of the original Nd content as pure neodymium and 55.0% of the original Pr content as pure praseodymium. In the experiment with the flow rate of 2.0 cm./min., the analyses indicated that fractions of the eluate contained 54.7% of the original Nd content as pure neodymium and 35.4% of the original Pr content as pure praseodymium.

EXAMPLE IX Three 22-mrn. columns, each containing Amberlite IR-lOO resin in a bed height of 120 cm. and having mesh size of -30, +40, were prepared.

Table VII Eluate R20 R30 EH0 H0203 Dy2oa Yzoz 1 GdzOa $11120 Ndz0 PlgO;

Grams per Lieggg Grla'ggs liter Per cent Per cent Per cent Per cent Per cent Per cent Per cent Per cent 388-443 5: 23 "6:655" '56' 15:5 513 a" II III: III III 443-482 5. 58 0.143 0 3 20 77 482-520 6.90 0.182 10 67.3 15 7.7 520-575 12.85 0.234 2 29.5 43.5 25 5754520 12.95 0.288 9.3 45.2 38 7.5 620-675 14.30 0.260 1.0 17.3 15.5 65.3 675-725 5.82 0.116 .1. 3 2 25 725-768 1.60 0.037 81 19 1 Yzoa determined by difference.

EXAMPLE VIII For each column 1.695 g. of a mixture of equal amounts of NdzOa and PlsOn was used to pre-.

pare an aqueous solution of these rare earths which were then adsorbed from the aqueous solution of their chlorides as in Example VIII. A

Pr content of the mixture was collected in last 0.1%- citric acid solution containing 0.1% phenol,

"andtammonium hydroxide having been added in sufficient quantity (320 ml. of vl H4.OH-solution in 45 l. of the citric acid'solution) to provide a pH of 5.5 was prepared. A second aqueous solution containing 0.05% citric acid, 0.1% phenol, and the same amount of ammonium hydroxide, which provided a pH of 8.63, was prepared. A third aqueous solution containing 0.025% citric acid, 0.1% phenol and the same amount of ammonium hydroxide, which provided a pH of 9.15 was prepared. These three citric acid solutions were passed through the three columns containing the adsorbed rare earths. In each case, the flow rate was 0.5 cmJmin.

The eluates fromthe column using the 0.1% citric acid showed a break-through or desorption of rare earth material at 30.5 1. The analyses of the fractions of the eluate showed the type of separation obtained in the experiment described in Example VIII using the same flow rate. The eluates'from the column using the 0.05% citric acid solutionas eluant showed a breakthrough of rare earth material between 39.1 and 39.5 1., at which point the pH of the eluate had risen to 3.5. Immediately subsequent fractions of "the eluate showed the pH of the eluate'was rising very rapidlyand the fraction between "42 and 42.5 1. had a pH M84. The fractions of the eluate showed some enrichment in this ex-- periment. The first 0.366-g. quantity of rare .earth values eluted contained less than 10% Pr. The first eluate'fraction contained 0.0147 g. R203 which analyzed 5.9% Pr. In the experiment using the 0.025% citric acid, there were no rare earth values present in any fraction of the eluate up to 53 1., even though the pH of the eluate had risen to 9.1 at 47.1.

The data in the experiments using 0.05% and 0.025%.citric acid, in conjunction with the data vof the other examples, indicate that 0.05% is about the minimumconcentration of citric acid for carrying out the. process of this inventionand that at about 0.05% citric acid the pH of the .eluant should be below 8.63, namely, should be no higher than about 7-0 to obtain at least an adequate partial separation of rare earth elements and preferably toobtain quantities .ofpure rare. earth element.

EXAMPLE .5!

.A .l.695-g..mixture of equal amounts of neodymium and .praseodymiumoxides was usedto prepare an aqueous. solution of their chlorides and the rare earths were adsorbed therefromasin Example VIII. However, the 120-cm. .height'of resin bed in.the..22-mm. column was 30, +40

mesh fDowex50 in'theacid cycle due to pre- EXAMPLE m A mixture, 1.71 g. as R203, of rare earth elements which analyzed 33.6% Sm2O3, 28.8% Nd203 and 34.7% PIsQn was adsorbedlfrom an aqueous solution of their chlorides :on. a .l20-cm. bed of 0.1% citricacid solution containing 0.1% phenol water-rinsed.

.and having .a pH of 5.30 due to the addition of ammonium hydroxide was passed through the column. .Fractions of the eluate were collected and analyzed for total rare earth content as well as "the individual rare earth elements. The resultant -data indicated that fractions oftheeluate were obtained which contained 80.2% of the original Sm content as pure samarium, 64.2% of the original Nd content as pure neodymium, and 71.8% of the original Pr content as pure praseodymium. The rare earth content of the first fractions of the eluate was pure samarium. In subsequent "fractions ofthe'e'lua te 'samarium was present with neodymium. These fractions contained decreasing amounts Of 'sama'ri .m values. After all of the samarium ha'd'been eluted, the next fractions of "the eluate contained-pure neodymium values. Still later fractions contained neodymium and praseodymium values. The final fractions of the eluate contained pure praseodymium values. IThetotal recovery of rare earth values by 'elution' was 9118 A 22-min. column containing a bedheightof cm. of .Nalcite HCR spheres having amesh of 30, +40 was prepared in the acid cycle and A mixture of neodymium and samarium was adsorbed from anaqueous solution of their-chloridespreparedfrom 1.713 g. of a mixture containing 50% NdzOs and- 50% 8111203. A 0.1% citric acid solutioncontaining 0.1% phenol and having a pH value of 6.30 due to the addition of ammonium hydroxide was then passed through the column at a flow rate of 0.25 cm./min. At an eluate volume of 37.9 1. the rare earth material was beginning to be eluted. Analyses of collected fractions of the eluate were made and the data indicated that the first rare earth-containing fractions contained 62.5% of the original Sm content as pure samarium. The intermediate fractions contained mixtures of samarium and neodymium values and the final fractions ofthe eluate contained 61.2% of the original Nd content as pure neodymium. The

total recovery of rare earth values from the resin by elution with the citric acid solution was 97.9%.

In an experiment .under identical conditions, except Dowex 50 spheres of 30, +40 mesh were used, fractions of the eluate contained 70.2% of the original \Sm content as pure samarium and other final fractions contained 70.9% of theoriginal Nd content as pure neodymium. The total recoveryof rare earth values from .theresin' byelutionwas 98.9%.

XIII

0.1% phenol and having a pH of 6.0;due to the .additirin nf ammonium. hydroxide was passed at a aflow'iizate inf .0. 25 cml/mm.

EXAMPLE XIV Three 4-in. columns were loaded with 30, +40 mesh Amberlite 112-100 resin each to a bed height of 4 it. On each column of resin rare earth materials were adsorbed from an aliquot of an aqueous solution having a pH of 1.8 and containing rare earth chlorides obtained by dissolution in hydrochloric acid of 286 g. of a material containing 39% Yb2O3, 12% T111203, ErzOs, 1% H0203, and 43% Lu and Y oxides (by difference). Through each column a 0.1% citric acid solution having a pH of 6.0 due to the addition of ammonium hydroxide was passed at a flow rate of 40 ml./min. The total volume of eluate from each column was about 780 l. The analyses of theeluate fractions showed that there was a total separation effected at least in some eluate fractions with regard to non-adjacent heavy rare earth elements and at least a fair degree of enrichment with respect to immediately adjacent heavy rare earth elements. Further treatment by the process of this invention of enriched mixtures will permit additional recovery of pure heavy rare earths.

EXAMPLE XV sorbed on each column in the amount of 1.4976 g.,

calculated as R203, in which the mixture was 49% Sm2O3 and 51% GdzOa. In one of the series of columns 0.5% citric acid solutions adjusted to various pH values with ammonium hydroxide were used as the eluant at various flow rates. In

the other series 0.1% citric acid solutions adjusted with ammonium hydroxide to various pH values were used as eluants at various flow rates. The various eluate fractions of both series of experiments were analyzed for total R203 content as well as Sm2Os and Gd203 content.

Assuming a theoretically complete separation of gadolinium and samarium, and graphically representing the amount eluted of cumulative rare earth material (R203) as the abscissa and the percent Sl'nzOs in the various eluted fractions of rare earth materials as the ordinate, the line would coincide with the abscissa until 0.764 g. of R203 had been eluted. Then this line for complete separation would rise verticall and indicate elution of pure Sm2Os. The curvewould remain at that level for the balance of the elution. Using the same coordinates, the line representing no separation in the elution would be a straight line at the 49% Sm2O3 level from initial elution until all of the R203 would be eluted. Upon plottinga curve for an experiment in which some separation or enrichment occurs, there is an area in the graph between the line for no separation and the curve from that experiment.

12 The ratio of that area to the area obtained by complete separation, multiplied by 100, is referred to in the following table as percent separation. This percent separation is an indication of the degree of enrichment obtained.

Table IX Per cent 0 M pH of he as? Acid in Eluant m1 lmi'n Eluant on O. 5 4. 5 2 9 0. 5 4. 4 2 11 0. 5 4. 4 1 9 0. 5 4. 3 2 10 0. 5 4. 2 2 9 0. 5 4. l 2 20 0. 5 4. 0 2 24 0. 5 3. 9 2 20 0. 5 3. 8 2 21 0. 5 3. 8 1 18 0. 5 3. 7 2 19 0. 5 3. 6 2 24 0. 1 5. 3 2 44 0. 1 5. 3 1 40 0. 1 5. 5 2 37 O. 1 5. 5 1 43 0. 1 5. 7 2 l7 0. 1 5. 7 1 22 J In an analogous experiment, using a 240-cm. bed height instead of the usual -cm. height and using 0.1% citric acid having a pH of 5.5 with a flow rate of 2 ml./min. there was 20% separation.

From the foregoing data of this example, it is apparent that 0.1% citric acid is preferred to 0.5% citric acid for increasing the degree of separation of heavy rare earth elements.

EXAIVIPLE XVI A series of columns was loaded with -30, +40 mesh cation exchange resin and on each a mixture of heavy rare earth elements was adsorbed from an aqueous solution of their salts. The aqueous solution for each adsorption was obtained from a 1.473-g. rare earth oxide sample that analyzed 19% DyzOs, 1% Sm2O3, 2% H0203, 4 Gd2O3, and 35% Y2O3. A series of 0.1% citric acid solutions adjusted to pH values between 5.7 and 6.3 was prepared. These solutions were used in a series of desorption experiments with the foregoing columns of resin containing adsorbed rare earth elements. The flow rate in all cases was 2 mL/min. The eluate fractions were analyzed and the dysprosium analyses were used as an indication of the degree of separation or enrichment obtained in these experiments. The dysprosium analyses were used in the same way as the samarium analyses were used in Example XV for determining the degree of separation,which was expressed as percent Dy separation. Table 13 analogous experiment was performed xus- I ing a GO-cm. be'd 'heightof -'60, +80. meshresin and using 0.1% citric acid at a:pH. of 6.0. There =was'38% Dy separation.

While-preferred "embodiments of the present invention "are described above, other modifications-maybe made without departing from the spirit and scope of the invention. Thus, :this invention is not to be limited to the examples but it is to be limited only Shy the appended claims.

This application is a continuation-impart of our copen'ding application Serial No. 769. ,326 filed August 18, 1947, now abandoned.

What is claimed is:

*1. "A-processfor the separationrof rare earths, :Which comprises contacting an aqueous sodution contain'ing Water-soluble inorganic salts of'rare earths with :a cation exchange resin 'to adsorb said rare earths on the resin, passing through a column of the adsorbed resin an aqueoussolution containing'from 0.05% to citric acidand having .a pHfrom 225 to 7.0, passing theeluate through a column of cation exchange :resin, *andrcollecting successive portions of the .resultant eluate.

32. sA'process for theseparation of rare earths, s-which-comprises passing an aqueous solution. con "taining water-soluble inorganic salts of rare earths through aeolumnoi cation exchange resin :to.adsorbsaid:rarerearths on part of the resin. passingthrough .thercolumn of the resin anaqueous solution containing from 0.05 to 5% citric .acid-andhaving:a,pI-I-,from 2.5 to 7.0, and col- .lectingsuccessive portions of the resultant eluate. 1 r

3. The process of claim 2 wherein the amount :Gf resin used is at least-5 times the amountrerquired toadsorb the rare earths.

A. :A process for the-separation of rare earths, whichcomprises passing .anaqueous solution conutaininga mixture of.rar.e earth chlorides through .acolur nof a .sulfonated synthetic organic cation exchange resin to adsorb .sai'd .rare earths .ornpart of the. resin,.passing through thecolumn .ofthe resinanagueous solution containing from a 0.05 to 5% citric acidand having a pH from 2.5 .to 7.0, and collecting successive portionsof .the .lesultant eluate.

5. A process for the separation of rare earths,

which comprises passing an aqueous solution ,con-

ltaining a mixture of rareearth chlorides through a column of a sul'fonated phenol-formaldehyde type of cation exchange resin "to adsorb said rare 'earths on part of the resin, passing through the column of the "re in an aqueous solution con- "8. A process'for the separation of rare-earths, I

--which comprises passing anaqueoussolution containing a mixture of rare earth chloridesthrough a :column of 'a nuclear sulfonic type 'of cation "ex- :change "resin toadsorb saidrare earths on part -iof the resin, passingthrough the column of the -resin-an aqueous solution containing from 0.05 105% citric acid and having .a pH from 2.51150 '7.0,-and collecting successive portions of the re- .zsultant eluate.

-' 9. ;A process for the separationofa immediately amass:

adjacentrare .earths,xwhich'comprises :passing::an aqueous :solution containing .a mixture of immediately adjacent .rareearth chlorides through .-:a column of .za'sulfonated phenol-formaldehydeitype of .cation exchange resin to :adsorb -said rare earths on part-of theresin, passing-through the columnof'the resinsan aqueous solution containing from.0.05 'to 5% citric .acid andhaving ;-a pH from 2.5 to 7.0, and collecting successive portions of the resultant eluate.

'10.':The' process .of claim 9 wherein the phenol used inithe preparation .of the resin .isra naturaloccurring phenolic compound.

11. .The process :,of claim 9 wherein the phenol used in the preparation .of the resin .is .a'syntheticphenolic compound.

12. A process for the separation of immediately adjacent .rare earths, which comprises passing an aqueous :solution containing a .mixture of immediately adjacent rare earth chloridesthrough a column of anuclear sulfonic-type of cation exchange resin to adsorb said rare earths .on :part of .the resin, passing through the column of the resin an aqueous solution containingfrom 0.05 to 5% citric acid-and havingga pI-I from'2.5 .to 7:0, and collecting successive portions of the resultant eluate.

13. Aprocess for the separation of neodymium and .praseodymium, which comprises passing an aqueoussolution of neodymium and praseodymiumichloridesthrough'a column :of :a cation exchange -resin to adsorb :said neodymium and praseodymium on part --of the resin, passing through the column of :the resin an aqueous solution containing from 0.05 to 5% citric acid and having arpH from 2.5 to 7.0,and collecting 'successiveportions of the resultant eluate.

1.4. A process for the separation of neodymium and praseodymium, which comprises passing an aqueous so ution of neodymium and praseodym ium chlorides through a column of a sulfonated phenol-formaldehyde type of cation exchange resin to adsorb said neodymium and praseodymium on part of the resin, passing through the column of the resin an aqueous solution containing from 0.05 to 5% citric acid and having a pH from 2.5 to 7.0,"and collecting successive portions of the resultant eluate.

15.'The process of claim 14 wherein'the citric acid solution contains 5% citric acid, and hasa :pH "from 2.5 to 3.0.

16. The process of claim 14 wherein the citric -acid-solution contains 0.5% citric acid and hasa .zpH ;from 3:5 to 4.5.

.17. The process-of claim 14 wherein the citric acid solution contains 0.1% citric acid and has a pH from 5.0 to 6.5.

18....A process for the separation of neodymium and praseodymium, which comprises passingan saqueousrsolution iOf neodymium and praseodymium :ohlorides through a column of a sulifona'tedsynthetic organic cation exchange resin "to 'adsorb said neodymium and praseodymium 'ion the-resin and wherein the amount of resinis at :least .15 times the amount required to adsorb :;a1l;.of the .neodymium andpraseodymium, pass- :ingzthrough the column of the resin an aqueous solution :containing fromflOE to 5% ,citric acid and havingiagpl-l'from 2.5 to 7.0, and collecting successive portionsof the resultant-eluate.

15 change resin to adsorb said neodymium and praseodymium on the resin and wherein the amount of resin is at least times the amount required to adsorb all of the neodymium and said neodymium and praseodymium on the resin and wherein the amount of resin is atleast 5 times the amount required to adsorb all of the neodymium and praseodymium, passing through the column of the resin an aqueous solution containing from 0.05 to 5% citric acid and having a pH from 2.5 to 7 .0, and collecting successive portions of the resultant eluate.

21. A process for the separation of neodymium and praseodymium, which comprises passing an aqueous solution of neodymium and praseodymium chlorides through a column of a sulfonated synthetic organic cation exchange resin to adsorb said neodymium and praseodymium on the resin and wherein the amount of resin is at least 5 times the amount required to adsorb all 1 of the neodymium and praseodymium, passing through the column of the resin an aqueous solution containing from 0.05 to 5% citric acid and having a pl-I from 2.5 to 7.0, and collecting a first portion of eluate containing neodymium of high purity, an intermediate portion of eluate containing a mixture of neodymium and praseodymium, and a final portion containing praseodymium of high purity.

22. A process for the separation of samarium and neodymium, which comprises passing an aqueous solution of samarium and neodymium chlorides through a column of a sulionated synthetic organic cation exchange resin to adsorb said samarium and neodymium on the resin and wherein the amount of resin is at least 5 times the amount required to adsorb all of the samarium and neodymium, passing through the column of the resin an aqueous solution containing from 0.05 to 5% citric acid and having a pH from 2.5 to 7.0, and collecting a first portion of eluate containing samarium of high purity, an intermediate portion of eluate containing a mixture of samarium and neodymium, and a final portion containing neodymium of high purity. I

23. The process of claim 22 wherein the citric acid solution contains 0.1% citric acid, and has a pH from 5.0 to 6.5.

24. A process for the separation of heavy rare earths, which comprises passing an aqueous solution of heavy rare earth chlorides through a column of a sulfonated synthetic organic cation exchange resin to adsorb said heavy rare earths on the resin and wherein the amount of resin is at least 5 times the amount required to adsorb all of the heavy rare earths, passing through the column of the resin an aqueous solution containing 0.1% citric acid and having a pH from 5.0 to 6.5, and collecting successive portions of the resultant eluate.

25. A process for the separation of rare earths, which comprises passing through a column of cation exchange resin containing a mixture of rare earths adsorbed on its upper part an aqueous solution containing from 0.05 to 5% citric acid and having a pH from 2.5 to 7.0, and collecting successive portions of the resultant eluate.

26. The process of claim 25 wherein the resin is a sulfonated synthetic organic cation exchange resin and the upper part of the resin constitutes less than one-fifth of the total quantity of resin.

27. The process of claim 26 wherein the citric acid solution contains 0.1% citric acid and has a pH from 5.0 to 6.5.

28. A process for the separation of rare earths, which comprises contacting an aqueous solution containing water-soluble inorganic salts of rare earths with a cation exchange resin to adsorb said rare earths on the resin, passing through a column of the adsorbed resin an aqueous solution containing from 0.5 to 5% citric acid and having a pH from 2.5 to 4.1, passing the eluate through a column of cation exchange resin, and collecting successive portions of the resultant eluate.

29. A process for the separation of rare earths, which comprises passing an aqueous solution containing water-soluble inorganic salts of rare earths through a column of cation exchange resin to adsorb said rare earths on part of the resin, passing through the column of the resin an aqueous solution containing from 0.5 to 5% citric acid and having a pH from 2.5 to 4.1, and collecting successive portions of the resultant eluate.

30. The process of claim 29 wherein the amount of resin used is at least 5 times the amount required to adsorb the rare earths. V

31. A process for the separation of rare earths, which comprises passing an aqueous solution containing a mixture of rare earth chlorides through a column of a sulfonated phenol-formaldehyde type of cation exchange resin to adsorb said rare earths on part of the resin, passing through the column of the resin an aqueous solution containing from 0.5 to 5% citric acid and having a pH from 2.5 to 4.1, and collecting successive portions of the resultant eluate.

32. The process of claim 3'1 wherein the phenol used in the preparation of the resin is a naturaloccurring phenolic compound.

33. The process of claim 31 wherein the phenol used in the preparation of the resin is a synthetic phenolic compound.

34. A process for the separation of immediately adjacent rare earths, which comprises passing an aqueous solution containing a mixture of immediately adjacent rare earth chlorides through a column of a sulfonated phenol-formaldehyde type of cation exchange resin to adsorb said rare earths on part of the resin, passing through the column of the resin an aqueous solution containing from 0.5 to 5% citric acid and having a pH from 2.5 to 4.1, and collecting successive portions of the resultant eluate.

35. The process of claim 34 wherein the phenol used in the preparation of the resin is a naturaloccurring phenolic compound.

36. The process of claim 34 wherein the phenol used in the preparation of the resin is a synthetic phenolic compound.

37. The process for the separation of neodymium and praseodymium, which comprises passing an aqueous solution of neodymium'and praseodymium chlorides through a column of a cation exchange resin to adsorb said neodymium and. praseodymium on part of the resin, passing through the column of the resin an aqueous solution containing from 0.5 to 5% citric acid and 

1. A PROCESS FOR THE SEPARATION OF RARE EARTHS, WHICH COMPRISES CONTACTING AN AQUEOUS SOLUTION CONTAINING WATER-SOLUBLE INORGANIC SALTS OF RARE EARTHS WITH A CATION EXCHANGE RESIN TO ADSORB SAID RARE EARTHS ON THE RESIN, PASSING THROUGH A COLUMN OF THE ADSORBED RESIN AN AQUEOUS SOLUTION CONTAINING FROM 0.05% TO 5% CITRIC ACID AND HAVING A PH FROM 2.5 TO 7.0, PASSING THE ELUATE THROUGH A COLUMN OF CATION EXCHANGE RESIN, AND COLLECTING SUCCESSIVE PORTIONS OF THE RESULTANT ELUATE. 